BURRUP PENINSULA, AUSTRALIA—A new study by geologist Brad Pillans of the Australian National University shows that engravings on Pilbara rocks from the Burrup Peninsula could last for 60,000 years. “The combination of hard rock and low rainfall means low erosion, so we have the potential for preserving rock art for much longer periods of time than in many other places,” he explained. People first reached Australia sometime between 35,000 and 42,000 years ago, so some of the estimated one million surviving petroglyphs may be tens of thousands of years old.